The present invention relates to inductive probes and the electronic package associated therewith for determining the level of a liquid metal in a chamber. More particularly, the probe employed is an inductively actuated bifilar wound coil which is disposed within the liquid metal bath. The primary winding of the coil is driven from a constant current source with the output signal developed in the bifilar secondary winding being a function of whether the secondary winding is effectively shorted by being immersed in the liquid metal.
Inductive bifilar wound coil probes for sensing liquid metal level are known in the art. Such inductive probes find particular application in sodium, and sodium-potassium systems which are currently under development for the breeder reactor program. These liquid metals are used as the primary coolant in such systems. A reliable and accurate means of determining the level of the liquid metal coolant in a given chamber must be provided. A large number of liquid metal level probes must be used in such systems to determine the level of the liquid metal in a variety of locations. The active length of the bifilar wound probe coil which is being used varies depending on the particular location of the probe and the degree of sensitivity and level range required for the particular sensing location. The electronic drive system is a constant current source which is transformer coupled to the probe so that a reasonable range of probe primary resistances can be driven without exceeding the range over which the current regulator will work. Thus, it is difficult to design a single electronic drive system which can be used for driving a very long coil length, as well as for driving a short coil length. The range of coil probe lengths, each of which requires a particular set of secondary taps from the drive transformer, could easily exceed the power capability of the electronic constant current drive unit coupled with the present secondary voltage measuring instrument so that desired accuracy cannot be maintained.
In prior art bifilar wound probe coils it has been the practice to operate the primary and secondary coils in a balanced configuration, that is with the coils being identical and with the wire diameter of the primary and secondary coils being the same. It is desirable to be able to vary sensitivity of a bifilar wound probe coil while permitting it to be utilized with the conventional constant current electronic drive system, which is also capable of driving a variety of other probe coils.